How severe is CVE-2026-12803?

CVE-2026-12803 has a CVSS 4.0 base score of 8.7, rated high severity.

Is CVE-2026-12803 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-12803?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-12803 published?

CVE-2026-12803 was published on 2026-08-03 and last updated on 2026-08-04.

CVE-2026-12803

CVE-2026-12803 is a high-severity vulnerability with a CVSS 4.0 base score of 8.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-354.

Key facts

Severity: High (CVSS 4.0 base score 8.7)
EPSS exploit prediction: 0% (7th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-354
Published: 2026-08-03
Last modified: 2026-08-04

Description

In Bouncy Castle for Java before 1.85, KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery). This issue also affects Bouncy Castle for Java LTS before 2.73.12.

Frequently asked questions

What is CVE-2026-12803?: In Bouncy Castle for Java before 1.85, KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery). This issue also affects Bouncy Castle for Java LTS before 2.73.12.
How severe is CVE-2026-12803?: CVE-2026-12803 has a CVSS 4.0 base score of 8.7, rated high severity.
Is CVE-2026-12803 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-12803?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-12803 published?: CVE-2026-12803 was published on 2026-08-03 and last updated on 2026-08-04.

References

Other CWE-354 vulnerabilities

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CVE-2017-15994 — Critical (CVSS 9.8): rsync 3.1.3-development before 2017-10-24 mishandles archaic checksums, which makes it easier for remote attackers to…
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CVE-2026-34182 — Critical (CVSS 9.1): Issue Summary: Cryptographic Message Services (CMS) processing fails to perform sufficient input validation on the…

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